The present invention relates to a disk cartridge enclosing a disk such as a magneto optical disk.
A conventional magneto optical disk cartridge encloses a rewritable magneto optical disk of 130 mm in diameter (5.25 inches), for example, in an approximately square flat case. The disk cartridge has a pickup hole for receiving an optical pickup on one side, and an external magnetic field hole for receiving an external magnetic field for recording and erasing on the opposite side at a position confronting the pickup hole. These holes on both sides of the cartridge are closed by a single U-shaped shutter.
However, this conventional shutter arrangement is not necessarily adequate for a magneto optical disk system of a type requiring a plurality of pickup holes in the disk cartridge. In order to increase the recording density in a system of a large-diameter magneto optical disk in which information is recorded at a revolving speed held constant, for instance, a plurality of pickup holes are required for recording and erasing of an inner annular area of the recording surface and for recording and erasing of an outer annular area so as to reduce the nonuniformity in density. In such a multi-perforated disk cartridge, it is difficult to open and close the pickup holes with only one shutter. Two conceivable arrangements to solve this problem are a multi-slide type and a rotary type. In the multi-slide type, however, a mechanism for sliding two or more shutters in combination is complicated and requires many constituent parts. In the rotary shutter, the support for rotation of the shutter must be provided around the center hole of the cartridge for receiving a turntable (a spindle motor). Therefore, this type requires another shutter for closing the center hole in addition to the rotary shutter for closing the pickup holes, and a complicated mechanism for moving both shutters in an interlocking manner.